The present invention relates generally to electrostatographic printing and/or reproduction devices, and more particularly to fuser apparatus comprising a donor roller having a polymeric surface layer thereon which is release agent swellable and resistant to toner contamination. The fuser apparatus is particularly useful for fusing toners prepared with relatively low-melting polymeric binder resins, such as polyester resins, employed in process color applications and/or high-speed printing or reproduction processes.
In the process of electrophotography, a light image of an original document to be printed or copied is typically recorded by either digital or analog means in the form of an electrostatic latent image upon a photosensitive member with subsequent rendering to make the latent image visible by application of electrostatically charged marking particles, commonly referred to as toner. The residual toner image can be either fixed directly upon the photosensitive member, or transferred from the photosensitive member to another support or receiver member, such as a sheet of plain paper, with subsequent affixing of the toner image thereto.
In order to fix or otherwise fuse the toner material onto a support member permanently, it is generally necessary to apply heat so as to elevate the toner material to a temperature at which constituents of the toner material coalesce and become tacky. This action causes the toner to flow to some extent into the fibers or pores of the support member or to otherwise adhere to the surface thereof. Thereafter, as the toner material cools, solidification occurs causing the toner material to be bound firmly to the receiver.
One method for thermal fusing of toner images onto a supporting substrate has been to pass the receiver with an unfused toner image thereon between a toning nip formed by a pair of opposed roller members that are in contact with each other, wherein at least one of the roller members is heated. During operation of a fusing system of this type, the receiver to which the toner image is electrostatically adhered is moved through the nip formed between the rolls with the toner image contacting the fuser roller thereby to affect heating of the toner image within the nip. Typical of such fusing devices are two roller systems wherein a fuser roller is coated with an abhesive material, such as a silicone rubber; other low surface energy elastomers, such as a Viton(copyright) fluoroelastomers available from E. I. DuPont De Nemours of Wilmington, Del.; or other low surface energy material, such as tetrafluoroethylene polymer resins like, for example, Teflon(copyright) resins also sold by DuPont. Silicone elastomers generally used to form a surface layer of the fuser member can be classified into three groups according to the vulcanization method and temperature employed to form such layer, i.e., room temperature vulcanization type silicone rubbers referred to as RTV silicone rubber; liquid silicone rubber referred to as LSR silicone rubber; and high temperature vulcanization type silicone rubber referred to as HTV rubber. These types of silicone elastomers are commercially available.
In the foregoing fusing systems, however, since the toner image is tackified by heat it frequently happens that a part of the image carried on the receiver will be retained by the heated fuser roller and not penetrate into the receiver surface. This tackified material can stick to the surface of the fusing roller and come in contact with a subsequent receiver sheet bearing another toner image to be fused. Thus, a tackified image which has been partially removed from a first sheet, may thereafter transfer to a subsequent second sheet in non-image portions of the second sheet. In addition, a portion of the tackified image of the second sheet may also adhere to the heated fuser roller. In this way and with the fusing of subsequent sheets bearing toner images, the fuser roller can eventually become thoroughly contaminated and unusable, thereby requiring replacement of the fuser roller itself. In addition, since the fuser roller continues to rotate when there is no substrate bearing a toner image to be fused, toner that may be adhered to the fuser roller can be transferred from the fuser roller to the pressure roller, and also to other rollers and components associated with the fuser system, thereby contaminating the overall fuser system. The foregoing conditions are referred to generally in the printing/copying art as xe2x80x9coffsetxe2x80x9d. Attempts have been made to control heat transfer to the toner and thereby control offset. However, even with abhesive surfaces provided by the silicone elastomers and the other materials mentioned hereinabove, this has not been entirely successful.
It has also been proposed to provide toner release agents such as silicone oil, and in particular poly(organosiloxane) oils like poly(dimethylsiloxane), that are applied to the surface of the fuser roller to act as a polymeric release agent and thereby reduce offset. The use of such release agents is reported, for example, in U.S. Pat. Nos. 3,964,431 and 4,056,706, the teachings of which are incorporated herein by reference. These release agents possess a relatively low surface energy and have been found generally suitable for use in a heated fuser roller environment. In practice, a thin layer of poly(organosiloxane) oil (also referenced as silicone oil hereinafter) release agent is applied to the surface of the heated fuser roller to form an interface between the fuser roller surface and the toner image carried on the support material. Thus, a low surface energy, easily parted layer is presented to the toners that pass through the fuser toning nip and thereby reduces the amount of toner which offsets to the fuser roller surface.
Some more recent developments in fuser rollers, polymeric release agents, and fusing systems are described in U.S. Pat. Nos. 4,264,181; 4,257,699; and 4,272,179, the teachings of which are also incorporated herein by reference. These patents describe fuser rollers and methods of fusing thermoplastic resin toner images to a substrate, wherein a poly(organosiloxane) type release agent having functional groups is applied to the surface of the fuser roller. The fuser roller employed generally consists of a base member having an elastomeric surface with a metal-containing filler material incorporated therein, wherein the elastomeric surface has been cured with a curing agent. Exemplary of such fuser rollers is an aluminum base member with a poly(vinylidenefluoride-hexafluoropropylene) copolymer (such as a Viton(copyright) type fluoroelastomer available from DuPont) cured with bisphenol curing agent and having lead oxide filler particles dispersed therein, and the fusing system generally utilizes a functionalized polyorganosiloxane oil as a polymeric release agent. In the disclosed fusing processes, the polymeric release agents have functional groups (also designated as chemically reactive functional groups) which are said to xe2x80x9cinteractxe2x80x9d with the metal-containing filler dispersed in the elastomer material of the fuser roller surface to form a thermally stable film. The film is said to release thermoplastic resin toner or otherwise hinder the thermoplastic resin toner from contacting the elastomer material of the fuser roller surface so as to reduce toner offset thereon. A metal oxide, metal salt, metal alloy or other suitable metal compound filler dispersed in the elastomer or resin on the fuser roller surface is said to interact with the functional groups of the polymeric release agent to create this condition. Preferably, the metal-containing filler materials do not cause degradation of or have any adverse effect upon the polymeric release agent having functional groups. Because of the interaction between the elastomer having a metal containing filler and the polymeric release agent having functional groups, excellent release and the production of high quality copies are said to be obtained.
In the foregoing patents, the interaction of the functionalized polymeric release agent with elastomer surface is said to be especially useful for offset reduction in non-silicone elastomer based fusing systems, such as those based on a Viton(copyright) fluoroelastomer.
U.S. Pat. Nos. 4,029,827; 4,101,686; 4,185,140; and 5,157,445, also incorporated herein by reference, disclose the use of functionalized polymeric release agents which are also said to interact with an elastomeric surface of a fuser roller to form a thermally stable, renewable self cleaning layer with allegedly superior release properties with respect to thermoplastic resin toners. In particular, U.S. Pat. No. 4,029,827 is directed to the use of poly(organosiloxane) oils having mercapto-functionality. U.S. Pat. Nos. 4,101,686 and 4,185,140 are directed to polymeric release agents having carboxy, hydroxy, epoxy, amino, isocyanate, thioether and mercapto functionality, while U.S. Pat. No. 5,157,445 is primarily directed to release agents having amino functionality.
According to the disclosed fusing methods, the toner release agents employed can be applied to the fuser roller by several delivery mechanisms including wicking, impregnating webs, and also by way of a so-called release agent donor roller. The donor roller may comprise a core of EPDM elastomer (a terpolymer of ethylene, propylene and diene monomers) with a thin surface layer thereover of polytetrafluoroethylene, such as Teflon(copyright) fluorocarbon resin available from Dupont, which is applied as an independent extruded thin sleeve bonded to said core.
Donor rollers comprised of a polytetrafluoroethylene sleeve bonded to an EPDM core are relatively expensive to make, and the manufacture of such a donor roll is tedious and inefficient, with the yield being relatively low since many of such sleeves are damaged during manufacture. Furthermore, in a fusing system such as that illustrated in FIG. 1 described hereinafter, such a sleeved release agent donor roller is largely ineffective in that since the release agent donor roller is driven by frictional engagement with the associated, positively-driven fuser roller, the hard, polytetrafluoroethylene surface coating of the donor roller with its relatively low coefficient of friction is not always adequately driven by the fuser roller.
Another technique used has been a donor roller having a surface layer including a HTV silicone elastomer material, such as that disclosed in U.S. Pat. No. 4,659,621. This patent discloses a release agent donor roller with a conformable donor surface thereon and consisting of a crosslinked addition curable vinyl terminated or vinyl pendant polyorganosiloxane. The patentees disclose that the HVT silicone elastomer surface of their donor roller exhibits a relatively low release agent swell rate over a relatively long period of time, with swell rates of generally less than 10 wt % being exemplified for examples said to correspond to the invention. While such silicone elastomer type donor rollers have been employed in some commercial applications, they still have a tendency to contaminate with toner resin due to offset, and this contamination problem is particularly a problem for toners which employ relatively low melting toner resin binders, such as polyester resins, currently used for process color printing or reproduction, and also for high speed printing or reproduction machines, such as speeds of greater than about 50 pages per minute and preferably greater than 100 pages per minute.
U.S. Pat. No. 6,190,771 B1 similarly discloses a relatively low swelling poly(organosiloxane) coated donor roller wherein the donor roller surface is a crosslinked, condensation polymerized poly(organosiloxane). While this donor roller can exhibit acceptable performance, due to its low swelling characteristic, it may also show a tendency to contaminate with toners that employ a relatively low melting polymer binder.
U.S. Pat. No. 5,061,965 describes a release agent donor roller made of a base roller, an intermediate comformable silicone elastomer layer, and a fluoroelastomer release layer thereover comprising a poly(vinylidenefluoride-co-hexafluoropropylene-co-tetrafluoroethylene) polymer and a metal oxide to interact with a functionalized polymeric release agent. While use of a fluoroelastomer surface with a functionalized release agent may minimize offset and contamination of the fuser system, such donor roller surface is susceptible to contamination anyway in the event of a failure in supply or distribution of the release agent itself, and it is also dependent on the ability of the release agent to wet the surface of the fluoroelastomer layer.
U.S. Pat. Nos. 5,141,788 and 5,166,031 disclose fuser members having an outer surface of a surface-grafted or volume-grafted hybrid of a fluoroelastomer and poly(organosiloxane), wherein said grafting is formed by dehydrofluorination of said fluoroelastomer by a nucleophilic dehydrofluorinating agent, followed by polymerization of an alkyl, alkene or alkyne functionalized poly(organosiloxane) with suitable polymerization initiators.
U.S. Pat. Nos. 6,067,438 and 6,075,966 disclose donor roller members with outer layers comprised of an interpenetrating network of fluorocarbon elastomer and poly(organosiloxane) polymers. Although donor rollers made using the materials disclosed in the foregoing patents may provide long life, they are also relatively more complex to manufacture and expensive to produce, and they are also essentially non-swelling with respect to the release agent, and thus, are susceptible to contamination anyway in the event of any failure in supply or distribution of the release agent itself, particularly where low melting point polymer toner binders are used.
As can be seen, it would be desirable to develop a donor roller which is relatively easy to manufacture and which is also not as dependent on the supply and/or distribution of release agent, but is resistant to contamination caused by offset of toner during fusing of images to a receiver, particularly for fusing of toners prepared with relatively low melting point resin binders.
The foregoing objects and advantages are achieved in one aspect by a release agent donor roller as described hereinafter for applying a polymeric release agent to a fuser roller in an electrophotographic apparatus. The donor roller comprises a base member with an outer polymeric layer thereover comprising a silicone material with a swelling in 300 cts poly(dimethylsiloxane) oil maintained at a temperature of 175xc2x0 C. after 24 hours of greater than 15% by weight.
In another aspect, the invention also relates to a fusing system for fusing toner to a receiver in an electrophotographic apparatus. The fusing system comprises:
(a) a fuser roller having an exterior surface and a pressure roller opposing said fuser roller and adapted to form a toning nip;
(b) a reservoir for holding a polymeric release agent;
(c) a metering roller adapted to receive a flow of the polymeric release agent from the reservoir; and
(d) a release agent donor roller for receiving the polymeric release agent from the metering roller and applying the polymeric release agent to the exterior surface of the fusing roller, the release agent donor roller comprising an outer layer of a silicone material with a swelling in 300 cts amine-functionalized poly(dimethylsiloxane) oil maintained at a temperature of 175xc2x0 C. after 24 hours of greater than 15% by weight.
In another aspect, the invention relates to a method for fusing a toner material comprised of a thermoplastic resin binder to a substrate. The method comprises:
forming a film of a release agent on the surface of a heated fuser member by contact of said fuser member with a release agent donor roller, the release agent donor roller comprising an outer layer of a silicone material with a swelling in 300 cts poly(dimethylsiloxane) oil maintained at a temperature of 175xc2x0 C. after 24 hours of greater than 15% by weight;
contacting the toner material on the substrate with the heated fuser member for a time sufficient to soften the toner material, and
allowing the toner material to cool.
In embodiments, the silicone material employed for the donor roller outer layer comprises a polymerized reaction product of:
(a) at least one cross-linkable poly(dialkylsiloxane);
(b) at least one cross-linking agent in an amount sufficient to yield a silicone material with a swelling in 300 cts poly(dimethylsiloxane) oil maintained at a temperature of 175xc2x0 C. after 24 hours of greater than 15% by weight;
(c) a minor amount of at least one particulate filler; and
(d) a cross-linking catalyst in an amount effective to react the poly(dialkylsiloxane) with the cross-linking agent.
In preferred embodiments, the silicone material comprises an addition polymerized reaction product of:
(a) at least one cross-linkable, vinyl-substituted poly(dialkylsiloxane) with a weight-average molecular weight before cross-linking of about 1,000 to about 90,000;
(b) from about 1 to less than 5 parts by weight per 100 parts of poly (diaklysiloxane) of finely divided filler; and
(c) at least one cross-linking agent comprising a multifunctional organo-hydrosiloxane having hydride functional groups capable of reacting with the vinyl functional groups of the poly(dialkylsiloxane); and
(d) at least one cross-linking catalyst present in an amount sufficient to induce addition polymerization of the poly(dialkylsiloxane) with the multifunctional organo-hydrosiloxane cross-linking agent.
An advantage of the present invention is that increasing the swell of the donor roller outer layer, such that swell is preferably controlled within a range as described hereinafter, will reduce toner offset, as well as maintain the mechanical properties of the release agent donor roller outer layer.
Another advantage of the present invention is that by increasing the oil swell of the donor roller outer layer through modifications to the chemical structure of the outer layer as described hereinafter, the outer layer can exhibit a lower coefficient of friction, thereby improving wear resistance and resulting in a longer useful roller life.